Many young men take up weight training because they are underweight. Individuals who have been underweight most of their lives usually have high metabolic rates, i.e., they burn calories at a rapid rate, making it difficult to add mass to their frames. Having such high BMR’s, these individuals are especially prone to overtraining. In such cases, the individual should train very hard with moderately heavy weights for a few sets per bodypart, and no more than three days a week. An underweight bodybuilder who wants to gain muscle and isn’t worried about adding a little fat must increase his caloric intake by as much as 500 calories a day above his daily maintenance needs. If he were to discover (using the method previously described) that his daily maintenance need is 5500 calories, he should up his daily intake by 500, making a total of 6000 calories a day.